Commonly, a conventional multilayer printed wiring board is made by alternately placing copper-clad laminates and sheets of prepreg one on another and integrating them. Such a multilayer printed wiring board has circuit patterns having outer layer pads formed therein, on the surfaces of the wiring board, and circuit patterns having inner layer pads formed therein, on the interlayer insulating layers of the wiring board.
These circuit patterns having these pads formed therein are electrically connected with each other via through holes drilled between each wiring layer in the direction of the thickness of the laminate.
However, for the above-mentioned multilayer printed wiring board having the through hole structure, areas for forming through holes need to be ensured. This imposes limitation to high-density packaging of electronic components. Thus, this poses problem that such a wiring board cannot sufficiently meet the requirements of microminiaturization of portable electronic equipment, and commercial use of a narrow pitch package and a multi chip module (MCM), for example.
For this reason, instead of such a multilayer printed wiring board having the through hole structure, a multilayer printed wiring board having an interstitial via hole structure throughout layers (hereinafter simply referred to as “IVH structure”) suitable for high-density packaging of electronic circuits has recently been drawing attention.
This multilayer printed wiring board having the IVH structure is structured so that each interlayer insulating layer constituting the laminate has via holes for electrically connecting circuits having pads formed therein.
Such a printed wiring board has the features in that the circuit patterns, each having inner layer pads formed therein, or the circuit pattern having inner layer pads and the circuit pattern having outer layer pads are electrically connected with each other by via holes that do not penetrate through the wiring board (buried via hole or blind via hole). Because of this structure, the multilayer printed wiring board having the IVH structure need not have the areas for forming through holes and each wiring layer can be connected by micro-via-holes only. This structure facilitates the miniaturization, higher-density packaging, and high-speed propagation of signals of electronic equipment.
Such a multilayer printed wiring board having the IVH structure is manufactured by the process shown in FIGS. 3A to 3E, for example.
As shown in FIG. 3A, used as prepreg 51 is a material made of aramid unwoven cloth impregnated with epoxy resin. First, this prepreg 51 is drilled using carbon dioxide gas laser. Then, this opening 52 is filled with electro-conductive paste 53.
Next, as shown in FIG. 3B, copper foils 54 are laminated on both sides of prepreg 51 and the laminate is heated and pressed using a hot press. Then, the epoxy resin and electro-conductive paste 53 in prepreg 51 are cured and copper foils 54 on both sides are electrically connected.
Next, copper foils 54 are patterned by etching to provide a hard double-side printed wiring board having a via hole as shown in FIG. 3C.
This double-side printed wiring board is used as a core layer. As shown in FIG. 3D, sheets of prepreg having electro-conductive paste filled therein and copper foils are positioned and successively laminated on both sides of the core layer. Then, the laminate is hot-pressed again and the copper foils 54 of the outermost layers are etched to provide a multilayer printed wiring board having a four-layer wiring structure, as shown in FIG. 3E.
For further multi-layered wiring, repeating the above-mentioned steps can provide a multilayer printed wiring board of six layers or eight layers.
However, the above-mentioned conventional technique has the following problems.
(1) For multi-layering, the process of lamination by hot-pressing and the process of patterning copper foils by etching need to be repeated many times. This makes the manufacturing process complicated and necessitates a considerable production time.
(2) For printed wiring boards having the IVH structure obtained by such a manufacturing method, patterning failure occurring even in only one part (one step) of the manufacturing process may cause the failure of the entire printed wiring board, i.e. a final product. This drastically reduces the yield thereof.
The present invention addresses such problems. Therefore, it is an object of the present invention to provide a laminating double-side circuit board that is suitable for production of a high-density multilayer printed wiring board having the IVH structure and capable of providing excellent electrical connection reliability of via holes for connecting wiring layers. It is another object of the present invention to provide a manufacturing method of the circuit board and a multilayer printed wiring board using the circuit boards.